P0573

What Does Code P0573 Mean?

DTC P0573 indicates a “Cruise Control/Brake Switch A Circuit High” condition, as detected by the Powertrain Control Module (PCM) or Engine Control Module (ECM). This code signifies that the PCM has received a voltage signal from the primary brake pedal position switch (often designated as ‘Switch A’ in diagnostic logic) that is continuously higher than the expected threshold, or high when it should be low, for a specified period or under certain operating conditions. In essence, the PCM interprets this high signal as the brake pedal being constantly applied, even when it is not, or as an open circuit where a normal operating voltage is detected but it’s outside the expected range. The brake pedal position switch serves a critical role, not only for illuminating the brake lights but also for providing input to numerous vehicle systems including cruise control disengagement, torque converter clutch (TCC) operation, automatic transmission shift interlock, and engine management strategies (e.g., fuel cut during braking). A persistent high voltage on this circuit can disrupt these crucial functions by providing false information regarding the driver’s braking intent.

Common Symptoms

• The Malfunction Indicator Lamp (MIL) illuminates on the dashboard.
• The cruise control system fails to engage or disengages unexpectedly.
• Brake lights may remain continuously illuminated, even when the brake pedal is not pressed, or may not illuminate at all.
• Difficulty shifting the transmission out of the Park position (for automatic transmissions).
• Inconsistent or harsh operation of the torque converter clutch.
• Potential interaction with Anti-lock Braking System (ABS) or Traction Control System (TCS) operation, though P0573 is primarily an ECM/PCM code.

What Causes the Code P0573?

• A faulty brake pedal position switch, which may be stuck in the “on” or “applied” position internally, or have an internal short causing a continuous high signal output.
• Corroded, damaged, or shorted wiring within the brake switch circuit, particularly a short to battery voltage or another power source, causing the PCM to see a constant high signal.
• Poor or intermittent electrical connection at the brake switch connector, including bent pins or terminal fretting corrosion.
• An improperly adjusted brake pedal position switch, where the switch plunger does not fully retract when the brake pedal is released, perpetually signaling an “applied” state.
• Less commonly, an internal fault within the Powertrain Control Module (PCM) or Engine Control Module (ECM), though this should only be considered after exhaustive diagnosis of the switch and wiring.

How to Diagnose and Troubleshoot

A systematic approach is crucial for diagnosing P0573.

1. Initial Scan and Data Review: Connect an OBD-II diagnostic scanner to confirm P0573 and check for any related or accompanying diagnostic trouble codes. Review freeze frame data to understand the engine conditions (RPM, vehicle speed, engine load, etc.) at the time the code was set.
2. Visual Inspection:
   • Inspect the brake pedal assembly for any obstructions that might prevent the pedal from fully returning to its rest position.
   • Locate the brake pedal position switch. Visually inspect its mounting and adjustment. Ensure the plunger or actuator of the switch fully extends and retracts with brake pedal movement.
   • Examine the electrical connector at the brake switch for signs of corrosion, damage, loose terminals, or improper seating.
   • Follow the wiring harness from the brake switch to the PCM (using a wiring diagram) and inspect for any visible signs of chafing, pinching, melting, or other damage that could indicate a short to power or an open circuit.
3. Brake Switch Circuit Voltage Test (using a Digital Multimeter – DMM):
   • Refer to the vehicle’s specific wiring diagram to identify the power supply, ground, and signal wires for the brake pedal position switch.
   • With the ignition ON, backprobe the brake switch connector (if accessible and safe) or disconnect the connector and test the power supply wire for battery voltage (B+).
   • Connect the switch and backprobe the signal wire while observing the DMM. With the brake pedal released, the signal voltage should be low (near 0V or a specified low voltage). When the brake pedal is pressed, the voltage should transition to high (near B+ or a specified high voltage). A “Circuit High” error suggests the signal line is continuously high even with the pedal released.
   • Alternatively, if the switch is a simple open/close type, check for continuity or resistance across the switch terminals in both activated and deactivated states to ensure proper operation. Some modern switches provide variable resistance or multiple signals; consult the service manual for expected values.
4. Wiring Integrity Test:
   • Disconnect the battery to prevent accidental shorts. Disconnect both the brake switch connector and the PCM connector (if safe and accessible).
   • Using the DMM in continuity mode, check for continuity in the signal wire from the brake switch connector to the PCM connector. Ensure resistance is minimal (typically less than 5 ohms).
   • Test the signal wire for shorts to ground by placing one DMM lead on the signal wire terminal and the other on a known good chassis ground. Resistance should be infinite (open circuit).
   • Test the signal wire for shorts to voltage by checking for continuity between the signal wire and any other power-carrying wires in the harness.
5. Live Data Monitoring: Using an advanced scan tool, access the live data stream and monitor the PID (Parameter ID) for the brake switch input or pedal position sensor. Observe its state (e.g., “Brake ON/OFF” or a voltage value) while manually operating the brake pedal. If the live data shows the brake switch as “ON” or a continuous high voltage even when the pedal is released, it confirms the PCM is receiving an erroneous signal.

Recommended Repairs and Solutions

• Replace the Brake Pedal Position Switch: If the diagnostic steps confirm the brake switch itself is faulty (e.g., stuck internally, incorrect voltage output), replacement is the most common solution. Ensure the new switch is correctly installed and adjusted according to manufacturer specifications. Improper adjustment can lead to recurring codes or incorrect brake light operation.
• Repair Wiring or Connectors: If the wiring inspection or DMM tests reveal a short to voltage, an open circuit, or excessive resistance in the brake switch circuit, perform precise wiring repair. Use appropriate gauge wire, solder connections, and protect with heat-shrink tubing. If the connector is damaged or corroded, replace the connector shell or individual terminals as needed.
• Adjust the Brake Switch: If the existing brake switch is mechanically sound but improperly adjusted, adjust its position so that it fully disengages when the pedal is released and engages correctly with minimal pedal travel. Refer to the factory service manual for specific adjustment procedures.
• PCM/ECM Replacement: Only consider replacing the PCM/ECM as a last resort, after thoroughly ruling out all possibilities related to the brake switch and its circuit. PCM replacement often requires specialized programming and is a costly repair.
• Post-Repair Verification: After completing any repairs, clear all stored DTCs using an OBD-II scanner. Perform a test drive, ensuring the cruise control system functions correctly, the brake lights operate as intended, and the MIL does not re-illuminate. Monitor live data for the brake switch input during the test drive to confirm proper signal transmission.